zipkin's tracingfilter doesn't work with 2.7

[beiwei30]

When I tried to add integration test for zipkin support on dubbo 2.7.x, I noticed the implementation of zipkin depends on the following old packages:

import brave.Span;
import brave.Span.Kind;
import brave.Tracer;
import brave.Tracing;
import brave.internal.Platform;
import brave.propagation.Propagation;
import brave.propagation.TraceContext;
import brave.propagation.TraceContextOrSamplingFlags;
import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.extension.Activate;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
import com.alibaba.dubbo.config.spring.extension.SpringExtensionFactory;
import com.alibaba.dubbo.remoting.exchange.ResponseCallback;
import com.alibaba.dubbo.rpc.Filter;
import com.alibaba.dubbo.rpc.Invocation;
import com.alibaba.dubbo.rpc.Invoker;
import com.alibaba.dubbo.rpc.Result;
import com.alibaba.dubbo.rpc.RpcContext;
import com.alibaba.dubbo.rpc.RpcException;
import com.alibaba.dubbo.rpc.protocol.dubbo.FutureAdapter;
import com.alibaba.dubbo.rpc.support.RpcUtils;
import java.net.InetSocketAddress;
import java.util.Map;
import java.util.concurrent.Future;

@Activate(group = {Constants.PROVIDER, Constants.CONSUMER}, value = "tracing")
// http://dubbo.apache.org/en-us/docs/dev/impls/filter.html
// public constructor permitted to allow dubbo to instantiate this
public final class TracingFilter implements Filter {
...
}

We should either consider to provide a new tracing filter for 2.7.0, or provide all compatible classes zipkin filter is using.

Adrian also mentions this particular issue here: openzipkin/brave#867 (comment)

[beiwei30]

64aea16

[chickenlj]

solved with 64aea16